{Contributed by W. Noakes)

Street Mains are generally laid in by the local Gas Company or their contractors, and are invariably cast iron. The size is, of course, in the discretion of the Gas Company, who provide as a rule for any estimated growth of the district by laying in a main of sufficiently large size against an increased consumption of several years ahead. The method of jointing usually adopted is the ordinary socket and spigot joint run with molten lead. The usual thicknesses of cast-iron mains are as follow: - Up to 9 inches diameter, § inch thickness of metal ; from 9 to 18 inches in diameter not less than \ inch thickness ; and over 18 inches diameter, 5/8 to 3/4 inch thickness of metal. Mains should be tested to withstand a pressure of not less than no lbs. per square inch.

Service Mains are sometimes of cast iron, as in the case of a large supply being required from the street main, but as a general rule the service from the street is of wrought iron, for it is not, as a rule, required over 3 inches diameter. Wrought iron in small sizes is much preferable to cast iron, not being so liable to fracture.

Where the service required from the street main is so large that a cast-iron pipe is used, the method of connecting the two pipes is as follows (see Fig 101). The fitter sets out on the main the length of the tee piece or junction which he has to connect, which we will assume to be 2 feet ; he then drills one hole on either side of the length thus marked on the main, into each of which he inserts a rubber bag with a pipe attached. He then inflates the bags and thus stops the passage of gas through the piece of pipe that he wishes to cut out. By means of a chisel he then cuts round the pipe at the points marked on the main, and a sharp blow on the pipe between the cuts will break the piece out, leaving room for the insertion of the junction. There will be one socket end on the junction into which one end of the main will fit, and the other socket is made by means of a loose collar, which is equal in length to about two ordinary sockets. This collar is slid on to the main or junction before the latter is inserted, and then, when the end of the junction is brought into line with the main, the collar is fixed to both main and junction by means of a lead joint at each end taking care that the joint between the main and junction is in the centre of the length of the collar. If it be inconvenient to shut off the main for the length of time required for making the joint a by-pass pipe may be fitted by drilling and tapping two holes in the main beyond the holes already made for the wind plug. Into each of these a bend is screwed, and the two are then connected by means of a connector or a short piece of pipe, thus allowing a constant supply to the other part of the main during the operation described above; and although a reduced supply only is provided it is generally sufficient for the time being. The holes in main made for plugging off and for by-pass must be stopped permanently with iron plugs before the main is again covered up.

Fig. ioi.

Fig. ioi.

As stated previously, the service mains are generally of wrought iron, and the operation of connecting these to the main is rather different to the foregoing (see Fig. 102). In this case a hole is either drilled or cut in the cast-iron main, and this is then tapped to receive the thread on the service pipe to be connected. This thread should always be given a slight taper towards the end to ensure a proper tight joint being made. A thick paint consisting of red and white lead is used for screwed joints to assist in making the joint quite sound. The common practice of using a considerable quantity of hemp in the joints to ensure their soundness is not to be commended, but the aim of the fitter should be to ensure perfect jointing by carefully cut threads, and by using as far as possible in one job the pipes and fittings of one maker only.

The laying of the pipes from the street into the house or meter house, after having made the connection on to the main, is very simple, being merely the forming of the ordinary screwed socketed joint. This is made in the following manner:- A socket, i.e. a short piece of pipe varying in length according to the size of the pipe, tapped at both ends to receive the external or male screw on the pipe, is screwed on to the end of the pipe already connected to the main, and into this is screwed the end of the next length of pipe, which also has a socket on its other end, and this operation is repeated until a sufficient length of pipe has been laid to reach to the meter house. This pipe is taken through the wall of the meter house, or whatever part of the building it is proposed to fix the meter in, and an iron-to-lead union is then screwed into the socket of the last pipe before reaching the meter; but before this union is put in the main service stop cock is usually fixed, as a means of shutting off the gas supply to the meter in case of repairs, removals, or for any other cause. This cock is provided and fixed by the local Gas Company, who also hold the key to it, and it should not be operated by anyone but a recognised official of the Company. It may be added here that while the Gas Company themselves generally run the main service and fit up the meter, except in the case of a very long distance existing between their main and the meter, they always put in the actual meter and the connections on the main side of the meter.

Gas Fitting 135

Fig. 102.

It should be borne in mind by the gasfitter during this stage of the work to make sure that no service pipe is too near the surface of the ground, especially where there is likely to be any heavy traffic, as it not infrequently happens that a steam roller or other very heavy vehicle strains and sometimes splits the pipe when passing over it, if it be placed too close to the surface. Although this is a matter under the direct supervision of the officials of the Gas Company, it is important enough to draw special attention to, as instances of neglect have led on more than one occasion to very serious and even fatal results.